A two-spray fungicide regime can be the most effective phoma control in oilseed rape when applied in the key risk period of mid- to late- October, the HGCA reports.
Small late-sown crops are most at risk of the disease which develops in warm and wet weather, and can cut yields by 0.5t/ha if the disease is not controlled.
“It is not looking likely there will be a big phoma disease year, but there is some potential for it to get worst if the weather turns mild and damp,” say Paul Gosling, research and knowledge transfer manager at the HGCA.
This season’s phoma risk forecast from Rothamsted Research predicts the high-risk period will be mid- to late- October for small crops.
If control is needed, the HGCA recommends a first fungicide spray is applied when 10-20% of plants show disease symptoms, and the second when there are visible signs of re-infection.
Fungicides with plant growth regulator activity, such as metconazole or tebuconazole. may be favoured where plants are large and reach 4-6 leaves in October, and have low levels of infection.
On the other hand, on smaller plants where curative activity is needed, prothioconazole or flusiazole products may be more appropriate to give good control.
Flusiazole is no longer on sale and all existing stocks must be used up by 12 October 2014.
Dr Gosling says half and full rates can give good phoma control, although the full rate is favoured when a high level of disease is seen.